1. Field of the invention
The subject invention relates to data processing and control, to data processing or bus system architectures, to bus line systems and methods for making same.
2. Disclosure statement
The following disclosure statement is made pursuant to the duty of disclosure imposed by law and formulated in 37 CFR 1.56(a). No representation is hereby made that information thus disclosed in fact constitutes prior art, inasmuch as 37 CFR 1.56(a) relies on a materiality concept which depends on uncertain and inevitably subjective elements of substantial likelihood and reasonableness, and inasmuch as a growing attitude appears to require citation of material which might lead to a discovery of pertinent material though not necessarily being of itself pertinent. Also, the following comments contain conclusions and observations which have only been drawn or become apparent after conception of the subject invention or which contrast the subject invention or its merits against the background of developments which may be subsequent in time or priority.
Despite a wide proliferation of data processing and system architectures, needs continue to persist in this area. Although the subject invention addresses itself primarily to microprocessor systems, it is not intended to be limited thereto, but obviously has considerably wider utility.
By way of background a typical microprocessor system architecture comprises data, address and control buses. The data bus carries information to and from the processor element, including instructions fetched from memory, data input from input devices, data stored in memory, and data output going to output devices. By way of example, the address proceeding over the address bus specifies where data are going or coming from, while the control bus is used to control sequencing and nature of operations being performed.
Reference may in this respect be had on standard texts about interfacing techniques, such as the SYBEX book on MICROPROCESSOR INTERFACING TECHNIQUES (2nd ed., 1977, 1978), by Austin Lesea and Rodney Zaks, which in Chapter 6 discusses bus standards and techniques. As an illustration of part of the problem, reference may be had to the following paragraph on page 273 of that book:
"What if a board is unplugged with the power on? The possibility of the -18 volts touching the +8 volts, due to misalignment, is great. If this happens . . . well, let us hope it doesn't. At best, only the regulators may blow out; at worst, every chip tied on +5 volts may be damaged."
The same may be said with respect to an accidental insertion of a circuit board in a reverse fashion, and with respect to similar mishaps.
There also are persistent needs for better system architectures in terms of interfacing peripherals with microprocessors, and in terms of improved busing systems, to name two examples.
In a similar vein, there have been past efforts to share the task of controlling various peripherals between two microprocessors. However, such efforts generally proceeded on an ad hoc basis, tailored to a particular problem. Also, such efforts typically employed a time-sharing concept which placed speed and efficiency limitations on the system. In other words, what was lacking was a systematic approach in terms of a generally applicable system architecture.